Indexeddb : How to limit number of objects returned?

Question

I'm using a cursor with a lower bound range query. I can't find a way to limit the number of objects returned, similar to a "LIMIT n" clause in a databse.

var keyRange = IDBKeyRange.lowerBound('');

Does it not exist ?

score 11 · Accepted Answer · answered Aug 28 '12 at 21:01

11

As you're iterating through the results, you can stop at any time. Something like this should work:

var results = [];
var limit = 20;
var i = 0;

objectStore.openCursor().onsuccess = function (event) {
  var cursor = event.target.result;
  if (cursor && i < limit) {
    results.push(cursor.value);
    i += 1;
    cursor.continue();
  }
  else {
    // Do something with results, which has at most 20 entries
    console.log(results);
  }
};

Also, in the special case where you are selecting based on a key that is made up of sequential numbers, you could use a keyRange to explicitly return only a certain range. But that's generally not the case.

answered Aug 28 '12 at 21:01

dumbmatter

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exactly, it's not my case. I implemented what you describe above but in my case the object store is quite large so it's really dumb to retrieve all the data from it... hence my question... – Philippe Girolami Aug 28 '12 at 21:25
The code I posted isn't retrieving all the data, just the first 20 objects. – dumbmatter Aug 29 '12 at 04:37
1

Yes you're right but is the cursor streaming the data out of the DB ? It may be preloading everything before handling it back to the JS engine. For example, the MySQL driver for Java does that. – Philippe Girolami Aug 29 '12 at 08:42
Not that I've studied the source code of Chrome and Firefox to validate this, but it is supposed to be streaming the data out as you request it. I would be quite surprised if that wasn't the case. – dumbmatter Aug 29 '12 at 14:37
3

Chrome uses heuristics to preload up to 100 objects. – dgrogan Aug 30 '12 at 01:25

score 2 · Answer 2 · answered Sep 07 '14 at 17:10

2

An important fix its replace:

if (cursor && i < limit) {

for

if (cursor && results.length < limit) {

Remember that its an async call, and it could be adding elements on "results" at the same time and "i" would not have the proper value.

answered Sep 07 '14 at 17:10

Hans Langer

49
2

score 0 · Answer 3 · answered Aug 28 '12 at 13:14

0

You can even search by range in indexedDB with IDBKeyRange.bound function

IDBKeyRange.bound(keyValueFrom, keyValueTo, false, true);

You can set the start value, end value and if you should include the start and end value in the returned items. In my case i want the first value of the range, however i want to exclude the last value.

For details of IDBKeyRange please visit the W3C IndexedDB page

answered Aug 28 '12 at 13:14

Deni Spasovski

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Thanks but that's not what I asked : I want bound(0,infinity) but return only the first N – Philippe Girolami Aug 28 '12 at 15:27
why do you want to list through all items if you don't need em? you can list first N items with IDBKeyRange.bound(0, N, false, true); – Deni Spasovski Aug 28 '12 at 15:34
1

I have no way of setting the upper bound to only return 5, the value being queried isn't a sequence – Philippe Girolami Aug 28 '12 at 21:24

Indexeddb : How to limit number of objects returned?

3 Answers3